1. Field of the Invention
The present invention relates to an image forming technique which uses color toner and transparent toner.
2. Description of the Related Art
In electrophotographic color image formation, it has recently been a known practice to increase glossiness of a formed image using a transparent toner in addition to conventional color toners such as yellow, magenta, cyan, and black toners. Conventionally, glossy prints are produced by fixing transparent and color toners simultaneously or by fixing a transparent toner after fixing color toners.
Examples of conventional techniques such as described above include a technique disclosed in Japanese Patent Laid-Open No. 2007-011028 described below.
However, there are limits to amounts of toner that can be applied to a recording material. In image forming regions, depending on the amounts of applied color toner, the amount of transparent toner will become nonuniform, causing the problem of gloss irregularities. FIGS. 10A to 10C are diagrams schematically showing amount-of-applied-toner control for cyan (C), magenta (M), yellow (Y), black (K), and transparent toners in image formation according to the conventional technique. Reference numeral 10002 denotes an amount-of-applied-toner limit which represents a limit to the amounts of toner which can be applied to a recording material 10001 by one fixing operation. In amount-of-applied-toner control 10003, the amount-of-applied-toner limit 10002 is reached by Y, M, C, and K, making it impossible to further apply a transparent toner. In amount-of-applied-toner control 10004 to 10007, the proportions of color toners (cyan (C), magenta (M), yellow (Y), and black (K)) are lower than in the amount-of-applied-toner control 10003. This makes it possible to apply the transparent toner within the amount-of-applied-toner limit 10002. In amount-of-applied-toner controls 10005, 10006, and 10007, the transparent toner can be applied uniformly (in FIG. 10A, the amount of applied transparent toner is taken as 1).
Gradation images in FIG. 10B schematically show results of image formation based on the amount-of-applied-toner control in FIG. 10A. A nonuniform glossy effect is observed in the gradation image 10011 in FIG. 10B because the transparent toner has been applied nonuniformly as in the case of the amount-of-applied-toner controls 10004 and 10005 (FIG. 10A), for example. The gradation image 10010 shows no glossy effect because the transparent toner has not been applied as in the case of the amount-of-applied-toner control (FIG. 10A).
On the other hand, when color toner and transparent toner are fixed separately, a uniform glossy effect is obtained because the transparent toner can be applied uniformly, but two fixing operations are required, causing the problem of misregistration between the color toner and transparent toner. This problem comes to the fore in image formation for text images.